Studies will continue on the Epstein-Barr Virus and its relation to malignant and non-malignant diseases. Special emphasis will be placed on the differentiation of additional antigen-antibody systems related to the virus, including search for humoral and cell mediated immune responses to EBV-transformed cells. In line with these aims, efforts will be made to study the differential development of various antigens in lytically infected cells as well as in cells undergoing transformation with the aid of immunofluorescence and immuno-electron microscopy. The available and any new methods for detection of EBV- related antibody responses will continue to be applied to longitudinal serologic studies on patients with EBV- associated diseases; that is, infectious mononucleosis, Burkitt's lymphoma and nasopharyngeal carcinoma as well as certain other malignant or non-malignant diseases in which enhanced antibody titers to EBV- associated antigens are often noted. These studies may confirm and extend the observations that changes in the antibody spectra and titers are referable to advancement of control of the diseases and thus may provide prognostic information and serve to monitor the effectiveness of therapeutic measures. In turn, such observation would support a causal rather than casual relation of EBV to given diseases.